Conventionally, as an infrared ray sensor to detect an infrared ray, for example, p-n junction diode in which an epitaxially grown HgCdTe film is formed on CdTe system compound semiconductor substrate such as CdTe substrate, CdZnTe substrate, and the like, to be used as a photodiode is known.
The substrate for epitaxial growth to form the epitaxially grown HgCDTe film is subjected to a mirror finish by a method disclosed for example in Patent Document 1. To put it concretely, the CdTe substrate for epitaxial growth is subjected to the following procedures: CdTe single crystal obtained by a vertical Bridgman method or the like is thinly cut; the thinly cut CdTe single crystal is lapped, etched, polished, and the like; and eventually final polishing to finish the wafer surface to be a minor surface is performed. There are for example, minor etching method and mirror polishing method, as the final polishing.
Further, in the Patent Document 1, mirror polishing solution which is suitable for the mirror polishing method is suggested, and thus a mirror surface with less waviness and surface anomalies can be obtained.
By the way, the substrate for epitaxial growth which has been subjected to the mirror finish in the above described method, is usually not used for the epitaxial growth immediately as it is, but is used for the epitaxial growth after having been stored for a predetermined period of time. At this point, the substrates for epitaxial growth are required to keep their surfaces clean, and thus, are stored in a state of being housed in a wafer storage container one by one. For example, Patent Document 2 discloses a wafer storage container which is suitable for storing the substrates for epitaxial growth.
In a case where the substrates for epitaxial growth are stored by being housed in the above mentioned wafer storage container, particles may be attached to the front and rear surfaces of the semiconductor wafer. Thus, generally, the wafer storage container in which wafers are housed is wrapped up by a laminated bag, the interior of the laminated bag is discharged with air so as to be filled with inactive gas such as nitrogen gas, or the like, and the laminated bag is sealed so as to block contact with external air. Therefore, the particles are prevented from entering into the wafer storage container from outside.
On the surface of the CdTe substrate which has been stored for the predetermined period of time, not a few oxidized films which prevent normal epitaxial growth are formed. Conventionally, an etching treatment by Br2 methanol is performed in order to remove the oxidized films as a pretreatment of the epitaxial growth.    Patent Document 1: JP-Tokukou-Hei-6-92278A    Patent Document 2: WO2005/112106A1